A fuel system incorporating a boost pump unit, a boost pump unit and method of pumping fuel are provided. The fuel system and boost pump unit are preferably self-priming and do not utilize an airframe mounted pump for supplying fuel for an aircraft combustor. The boost pump unit includes a liquid ring pump and an air/fuel separator. The air/fuel separator has an inlet and first and second outlet ports. The inlet is operably fluidly coupled to an outlet of the liquid ring pump. The air/fuel separator has an arcuate flow path. The first outlet port is in fluid communication with a radially outer portion of the arcuate flow path and the second outlet port is in fluid communication with a radially inner portion of the arcuate flow path. A return line connected to the first outlet port is configured to return fuel to the liquid ring pump.